The production of near photographic quality images using electrophotographic imaging technology is highly desirable. It is even more desirable to produce such images on substrates that render the print with the look and feel of a typical photographic print produced with silver halide imaging technology, such as the degree and uniformity of glossiness, stiffness and opacity, and high resolution and sharpness with corresponding low grain appearance. The advantages to producing photographic quality images on such substrates using digital electrophotography include improved environmental friendliness, ease of use, and versatility for customizing images, such as when text and images are combined. When such glossy images can be combined with pen or pencil writability on the side opposite the glossy image, several applications can be envisioned such as photo quality calendars, greeting cards and postcards among others.
U.S. Patent Application 2002/0037176 A1 discloses a receiver sheet provided with a special coating on the backside to enable writablilty but no mention is made of the ability to write on the backside after printing on that side. Similarly U.S. Pat. No. 5,658,677 discloses a one-sided image carrier where the backside is coated with silica rich coatings to impart writability. These constructions, while very useful, do not lend themselves to the manufacture of two-sided writable sheets where both sides can be imaged and where one side can be selectively glossed. Such a paper would lend itself to a variety of other two-sided printed products such as calendars, postcards and greeting cards where only one image bearing side is glossed while the other printed side has to be writable.
U.S. Pat. No. 5,846,637 describes a coated xerographic photographic paper comprised of (1) a cellulosic substrate; (2) a first antistatic coating layer in contact with one surface of the substrate; (3) a second toner receiver coating on the top of the antistatic layer, and comprised of a mixture of a binder polymer, a toner spreading agent, a lightfastness inducing agent, a biocide, and a filler; and (4) a third traction controlling coating in contact with the back side of the substrate comprised of a mixture of a polymer with a glass transition temperature of from between about −50° C. to about 50° C., an antistatic agent, a lightfastness agent, a biocide and a pigment. This paper provides for the third layer on the backside of the substrate to receive toner, but this is not sufficient for ensuring high image quality should the image be created on this third layer instead of the second layer on the other surface of the substrate.
European Patent Application 1,336,901 A1 describes an electrophotographic image receiving sheet with a toner image receiving layer containing a release agent and formed on a support sheet for use in a fixing belt type electrophotography. The support used in the examples had a paper base with polyethylene layers on either side, where the image side is glossy and the backside has a matte finish. No provision is made for receiving the toner image on the backside.
US Patent Application 2003/0082354 A1 discloses an image receiving sheet for electrophotography comprising a base paper and a toner image receiving layer comprising a thermoplastic resin and less than 40 percent by mass based on the thermoplastic resin, of a reinforcing filler pigment. The thermoplastic layer is infiltrated to a depth of 1 to 50 percent of the thickness of the base paper. It is desirable that the toner image receiving layer is substantially free of any pigment or filler in order to prevent blister formation and roughening of the toner image.
US Patent Application 2003/0235683 A1 discloses an electrophotographic image receiving sheet comprising a support and a toner image receiving layer containing a thermoplastic resin and a pigment disposed on the surface of the support wherein the surface of the support has a glossiness of 25 percent or more at 75° and a pigment content less than 40 percent by mass based on the mass of the thermoplastic resin. In this case also it is desirable that the toner image receiving layer be substantially free of any pigment or filler in order to prevent blister formation.
Toner particle size also plays a key role in determining image quality in electrophotography, smaller particles generally yielding better image quality. However, as the particles get smaller, the physics of the forces holding the particles to the photoconductor changes drastically, needing new methods to effectively transfer them from the photoconductor to the receiver. Photographic quality prints can be produced with this process if very small toner particles are used. The drawback with small particles is the difficulty in transferring them onto plain paper. One solution to this problem is explained in U.S. Pat. No. 4,968,578, where the surface of the receiver sheets are coated with a thermoplastic layer.